The 906 lore is that the “F” heads are the best.

My findings have been that not all F heads are anything special........ however the best untouched 906 I’ve tested was indeed an F head.

What’s odd is it’s not like there are A, B, C, D heads.........I seem to recall C, F, M, R, and no letter for 906’s.

68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads